The present invention relates generally to a chain having a number of interleaved rows of link plates articulately connected together in an endless fashion by means of rocker joint pins, and more particularly to a chain having an improved rocker pin joint structure.
A chain having a number of interleaved rows of link plates articulately connected together in an endless fashion by means of rocker joint pins is used as a silent chain or a CVT (Continuously Variable Transmission) chain. The silent chain is used as a driving chain for an engine camshaft, or a power-transmitting chain for a transmission. The CVT chain is used as a power-transmitting chain for a CVT unit.
These chains essentially comprise a plurality of interleaved rows of link plates connected together in an endless fashion by rocker joints each composed of a pair of rocker joint pins of different lengths. The link plates each have a pair of pin holes. A longer pin and a shorter pin jointly forming one rocker joint are inserted through the respective pin holes in the link plate of one row and the respective pin holes in the link plate of an adjacent row so as to join the two adjacent link plate rows.
The pin holes of the conventional chain have a generally circular shape. The inner peripheral surface of the generally circular pin hole includes a chord-like seat surface located closer to an outer end of the link plate than to the center of the link plate. The longer pin and the shorter pin have the same cross-sectional shape and each include a convexly arcuate rolling surface. These pins are inserted through laterally aligned pin holes of the overlapping link plates in such a manner that the respective rolling surfaces of the longer and shorter pins are in confrontation with each other with the longer pin being seated on the seat surface of the pin hole in one link plate, and the shorter pin being seated on the seat surface of the pin hole in an adjacent link plate.
The chain of the foregoing construction, when used as a silent chain for an automobile, is required to have high wear resistance, great noise reduction and good lubricating properties in addition to easy assembly and producibility, and low cost.
In order to improve wear resistance, an attempt has been made to provide a large space for holding a lubricating oil between upper and lower portions of the outer peripheral surface of each pin and corresponding upper and lower portions of the inner peripheral surface of the pin hole. This prior attempt has not been satisfactory because the rocker joint pins are liable to displacement within the pin holes when they are designed to have a relatively small thickness for enabling adjustment of the chain pitch during assembly, or when they becomes thin due to progressive wear.
Once the rocker joint pins are displaced from the correct position within the pin holes, it becomes no longer possible for the respective rolling surfaces to contact with each other on a pitch line of the chain. Even though a large lubricating oil holding space is provided for improving wear resistance, wear has occurred with rocker joint pins and link plates due to interference between the displaced rocker joint pins and the inner peripheral surfaces of the pin holes.
In addition, since the respective rolling surfaces of the longer and shorter pins contact each other at an incorrect position, wear on the rolling surfaces is locally intensified, causing deterioration of the durability of the chain. The contact of the rolling surfaces at incorrect positions gives rise to the additional problem that the link plates are displaced or offset from the pitch line and hence unable to start meshing with a sprocket at a correct position. This will result in a remarkable increase in operation noise.
Japanese Utility Model Laid-open Publication No. 62-196950 and Japanese Patent No. 2924915 disclose a chain wherein a projection is provided at an upper portion or a lower portion of the inner peripheral surface of each pin hole so as to prevent displacement including rotation of rocker joint pins within the pin hole and also to prevent adjacent link plates from becoming bent into a V shape. By the projection thus provided, the rocker joint pins are held in position against displacement relative to the link plates.
However, the projection gives rise to another problem. The effective contact area between respective rolling surfaces of the longer and shorter pins is reduced by the projection, and the wear resistance of the chain deteriorates with a reduction of the effective contact area. In addition, since the projection partly surrounds the contour of each rocker joint pin, a space for holding a lubricating oil, defined between the opposed rolling surfaces, is reduced. This may accelerate wear of the rolling surfaces due to insufficient lubrication. Furthermore, due to the presence of the projection, placement of the rocker joint pins into the pin holes is not easy to achieve, thereby lowering the assembly efficiency and increasing the assembly cost. In addition, the presence of the projection makes it difficult to produce the link plates by punching due to a shortened service life of punching dies. This may add to the cost of the chain.
It is accordingly an object of the present invention to provide a chain having an improved rocker pin joint structure which is capable of holding rocker joint pins in a correct position against displacement relative to link plates.
Another object of the present invention is to provide a rocker pin joint structure of a chain, having a combination of a unique profile of the pin holes and a unique cross-sectional shape of the rocker joint pins, which is capable of preventing warping or reverse bend of the chain.
A further object of the present invention is to provide a chain having an improved rocker pin joint structure capable of withstanding a great load.
According to the present invention, there is provided a chain comprising a plurality of interleaved rows of link plates articulately connected together in an endless fashion by means of rocker pin joints. Each of the link plates has a pair of pin holes. Each of the rocker pin joints is composed of a pair of rocker joint pins inserted through each of the pair of pin holes in one link plate and each of the pair of pin holes in an adjacent link plate. The pair of rocker joint pins has a convexly arcuate rolling surface, a back surface opposite to the rolling surface, and a pair of upper and lower flat surfaces formed between the rolling surface and the back surface and extending in a longitudinal direction of the chain. Each of the pin holes has a seat surface engaged with the back surface and formed on a side located closer to an outer end of each link plate than to a center of the link plate, a pair of upper and lower pin-position constraining surfaces facing the upper and lower flat surfaces, respectively, of one of the pair of rocker joint pins seated on the seat surface with a very small clearance defined between each of the flat surfaces and a corresponding one of the pin-position constraining surfaces, a bend permitting surface contiguous to the upper pin-position constraining surface and spaced from the upper flat surface of the other rocker joint pin seated on the seat surface of the pin hole in the adjacent link plate, a warp blocking surface contiguous to the lower pin-position constraining surface and facing the lower flat surface of the other rocker joint pin seated on the seat surface of the pin hole in the adjacent link plate with a very small clearance defined therebetween, and a concavely arcuate surface contiguous to the bend permitting surface and the warp blocking surface and spaced from the back surface of the other rocker joint pin seated on the seat surface of the pin hole in the adjacent link plate.
When the chain is stretched substantially straight, the rocker joint pins are in contact with each other at their rolling surfaces within the pin holes of the two adjacent link plates.
Assuming that the one rocker joint pin is a longer pin and the other rocker joint pin is a shorter pin, the back surface of the longer pin is seated on the seat surface of a first link plate of the two adjacent link plates, and the back surface of the shorter pin is seated on the seat surface of a second link plate of the two adjacent link plates. The upper and lower flat surfaces of the longer pin face the upper and lower pin-position constraining surfaces, respectively, of the first link plate with a very small clearance being defined between each of the flat surfaces and a corresponding one of the pin-position constraining surfaces, so that the longer pin is prevented from moving in a vertical direction relative to the first link plate. The upper and lower flat surfaces of the shorter pin face the upper and lower pin-position constraining surfaces, respectively, of the second link plate with a very small clearance being defined between each of the flat surfaces and a corresponding one of the pin-position constraining surfaces, so that the shorter pin is prevented from moving in a vertical direction relative to the second link plate. Accordingly, when the chain in stretched substantially straight, both the longer pin and the shorter pin are held in position against vertical displacement relative to the first and second link plates. The respective rolling surfaces of the longer and shorter pins are, therefore, able to contact with each other at a correct position, so that they are free from local wear. In addition, the chain, while in a stretched condition, does not cause whipping or waving, thus reducing noises produced when the chain comes into meshing engagement with the sprocket.
The very small clearance provided between the upper flat surface of each rocker joint pin and the upper pin-position constraining surface of each link plate is indispensable for enabling placement of the rocker joint pins into the pin holes to thereby articulately join two adjacent link plates. The clearance is determined in view of manufacturing tolerances of the link plates and the rocker joint pins and should preferably be as small as possible.
When the chain is about to travel around the sprocket, the first link plate, for example, comes into meshing engagement with the sprocket before the second link plate. This movement causes the first link plate to turn or pivot about a common center of the pin holes of the first and second link plates. In this instance, the longer pin, seated on the seat surface of the first link plate, rolls on the rolling surface of the shorter pin which is seated on the seat surface of the second link plate. The upper pin-position constraining surface of the first link plate and the upper flat surface of the longer pin angularly move in phase with each other. During that time, the angular movement of the upper flat surface of the longer pin caused due to pivotal movement of the first link is permitted or accommodated by the bend permitting surface of the second link plate because the bend permitting surface is spaced from the upper flat surface of the longer pin when the chain is stretched substantially straight.
In addition, since the back surface of the longer pin is spaced or separated from the concavely arcuate surface of the second link plate, angular movement of the back surface, occurring when the first link plate is caused to turn relative to the second link plate, is permitted.
The chain as it is in the stretched straight state is sometimes forced to warp or bend about a rocker pin joint into a V shape. Such warping of the chain is prevented from occurring by means of the warp blocking surface of the present invention. For instance, when the first link plate is urged to turn or pivot in the reverse direction about the common center of the pin holes of the first and second link plates, the longer pin is gripped between the upper pin-position constraining surface of the first link plate and the warp blocking surface of the second link plate because the upper and second flat surfaces of the longer pin face the upper pin-position constraining surface of the first link plate and the warp blocking surface of the second link plate, respectively. At the same time, the short pin is gripped between the upper pin-position constraining surface of the second link plate and the warp blocking surface of the first link plate because the upper and second flat surfaces of the shorter pin face the upper pin-position constraining surface of the second link plate and the warp blocking surface of the first link plate, respectively.
In one preferred form of the present invention, the upper and lower pin-position constraining surfaces of each of the pin holes are formed on one side of a vertical centerline of the pin hole which is located closer to the outer end of each link plate than to the center of the link plate, and the bend permitting surface and the warp blocking surface are formed on the other side of the vertical centerline, which is located closer to the center of the link plate than to the outer end of the link plate.
It is preferable that the upper and lower flat surfaces of each rocker joint pin are straight and parallel with each other, and the upper and lower pin-position constraining surfaces of each pin hole are straight and parallel with each other. The warp blocking surface may be straight and symmetrical with the straight lower pin-position constraining surface about the vertical centerline of the pin hole. The upper and lower pin-position constraining surfaces may be sloping down toward the outer end of the link plate. Further, the bend permitting surface may be straight and extend at an angle to the upper pin-position constraining surface in such a manner that the bend permitting surface gradually retreats from the upper pin-position constraining surface in a radial outward direction of the pin hole.